package com.dream.utils.file;

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.Stack;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class DiffMatchPatch {
		// Defaults.
	  // Set these on your diff_match_patch instance to override the defaults.

	  /**
	   * Number of seconds to map a diff before giving up (0 for infinity).
	   */
	  public float Diff_Timeout = 1.0f;
	  /**
	   * Cost of an empty edit operation in terms of edit characters.
	   */
	  public short Diff_EditCost = 4;
	  /**
	   * At what point is no match declared (0.0 = perfection, 1.0 = very loose).
	   */
	  public float Match_Threshold = 0.5f;
	  /**
	   * How far to search for a match (0 = exact location, 1000+ = broad match).
	   * A match this many characters away from the expected location will add
	   * 1.0 to the score (0.0 is a perfect match).
	   */
	  public int Match_Distance = 1000;
	  /**
	   * When deleting a large block of text (over ~64 characters), how close do
	   * the contents have to be to match the expected contents. (0.0 = perfection,
	   * 1.0 = very loose).  Note that Match_Threshold controls how closely the
	   * end points of a delete need to match.
	   */
	  public float Patch_DeleteThreshold = 0.5f;
	  /**
	   * Chunk size for context length.
	   */
	  public short Patch_Margin = 4;

	  /**
	   * The number of bits in an int.
	   */
	  private short Match_MaxBits = 32;

	  /**
	   * Internal class for returning results from diff_linesToChars().
	   * Other less paranoid languages just use a three-element array.
	   */
	  protected static class LinesToCharsResult {
	    protected String chars1;
	    protected String chars2;
	    protected List<String> lineArray;

	    protected LinesToCharsResult(String chars1, String chars2,
	        List<String> lineArray) {
	      this.chars1 = chars1;
	      this.chars2 = chars2;
	      this.lineArray = lineArray;
	    }
	  }


	  //  DIFF FUNCTIONS


	  /**
	   * The data structure representing a diff is a Linked list of Diff objects:
	   * {Diff(Operation.DELETE, "Hello"), Diff(Operation.INSERT, "Goodbye"),
	   *  Diff(Operation.EQUAL, " world.")}
	   * which means: delete "Hello", add "Goodbye" and keep " world."
	   */
	  public enum Operation {
	    DELETE, INSERT, EQUAL
	  }

	  /**
	   * Find the differences between two texts.
	   * Run a faster, slightly less optimal diff.
	   * This method allows the 'checklines' of diff_main() to be optional.
	   * Most of the time checklines is wanted, so default to true.
	   * @param text1 Old string to be diffed.
	   * @param text2 New string to be diffed.
	   * @return Linked List of Diff objects.
	   */
	  public LinkedList<Diff> diff_main(String text1, String text2) {
	    return diff_main(text1, text2, true);
	  }

	  /**
	   * Find the differences between two texts.
	   * @param text1 Old string to be diffed.
	   * @param text2 New string to be diffed.
	   * @param checklines Speedup flag.  If false, then don't run a
	   *     line-level diff first to identify the changed areas.
	   *     If true, then run a faster slightly less optimal diff.
	   * @return Linked List of Diff objects.
	   */
	  public LinkedList<Diff> diff_main(String text1, String text2,
	                                    boolean checklines) {
	    // Set a deadline by which time the diff must be complete.
	    long deadline;
	    if (Diff_Timeout <= 0) {
	      deadline = Long.MAX_VALUE;
	    } else {
	      deadline = System.currentTimeMillis() + (long) (Diff_Timeout * 1000);
	    }
	    return diff_main(text1, text2, checklines, deadline);
	  }

	  /**
	   * Find the differences between two texts.  Simplifies the problem by
	   * stripping any common prefix or suffix off the texts before diffing.
	   * @param text1 Old string to be diffed.
	   * @param text2 New string to be diffed.
	   * @param checklines Speedup flag.  If false, then don't run a
	   *     line-level diff first to identify the changed areas.
	   *     If true, then run a faster slightly less optimal diff.
	   * @param deadline Time when the diff should be complete by.  Used
	   *     internally for recursive calls.  Users should set DiffTimeout instead.
	   * @return Linked List of Diff objects.
	   */
	  private LinkedList<Diff> diff_main(String text1, String text2,
	                                     boolean checklines, long deadline) {
	    // Check for null inputs.
	    if (text1 == null || text2 == null) {
	      throw new IllegalArgumentException("Null inputs. (diff_main)");
	    }

	    // Check for equality (speedup).
	    LinkedList<Diff> diffs;
	    if (text1.equals(text2)) {
	      diffs = new LinkedList<Diff>();
	      if (text1.length() != 0) {
	        diffs.add(new Diff(Operation.EQUAL, text1));
	      }
	      return diffs;
	    }

	    // Trim off common prefix (speedup).
	    int commonlength = diff_commonPrefix(text1, text2);
	    String commonprefix = text1.substring(0, commonlength);
	    text1 = text1.substring(commonlength);
	    text2 = text2.substring(commonlength);

	    // Trim off common suffix (speedup).
	    commonlength = diff_commonSuffix(text1, text2);
	    String commonsuffix = text1.substring(text1.length() - commonlength);
	    text1 = text1.substring(0, text1.length() - commonlength);
	    text2 = text2.substring(0, text2.length() - commonlength);

	    // Compute the diff on the middle block.
	    diffs = diff_compute(text1, text2, checklines, deadline);

	    // Restore the prefix and suffix.
	    if (commonprefix.length() != 0) {
	      diffs.addFirst(new Diff(Operation.EQUAL, commonprefix));
	    }
	    if (commonsuffix.length() != 0) {
	      diffs.addLast(new Diff(Operation.EQUAL, commonsuffix));
	    }

	    diff_cleanupMerge(diffs);
	    return diffs;
	  }

	  /**
	   * Find the differences between two texts.  Assumes that the texts do not
	   * have any common prefix or suffix.
	   * @param text1 Old string to be diffed.
	   * @param text2 New string to be diffed.
	   * @param checklines Speedup flag.  If false, then don't run a
	   *     line-level diff first to identify the changed areas.
	   *     If true, then run a faster slightly less optimal diff.
	   * @param deadline Time when the diff should be complete by.
	   * @return Linked List of Diff objects.
	   */
	  private LinkedList<Diff> diff_compute(String text1, String text2,
	                                        boolean checklines, long deadline) {
	    LinkedList<Diff> diffs = new LinkedList<Diff>();

	    if (text1.length() == 0) {
	      // Just add some text (speedup).
	      diffs.add(new Diff(Operation.INSERT, text2));
	      return diffs;
	    }

	    if (text2.length() == 0) {
	      // Just delete some text (speedup).
	      diffs.add(new Diff(Operation.DELETE, text1));
	      return diffs;
	    }

	    String longtext = text1.length() > text2.length() ? text1 : text2;
	    String shorttext = text1.length() > text2.length() ? text2 : text1;
	    int i = longtext.indexOf(shorttext);
	    if (i != -1) {
	      // Shorter text is inside the longer text (speedup).
	      Operation op = (text1.length() > text2.length()) ?
	                     Operation.DELETE : Operation.INSERT;
	      diffs.add(new Diff(op, longtext.substring(0, i)));
	      diffs.add(new Diff(Operation.EQUAL, shorttext));
	      diffs.add(new Diff(op, longtext.substring(i + shorttext.length())));
	      return diffs;
	    }

	    if (shorttext.length() == 1) {
	      // Single character string.
	      // After the previous speedup, the character can't be an equality.
	      diffs.add(new Diff(Operation.DELETE, text1));
	      diffs.add(new Diff(Operation.INSERT, text2));
	      return diffs;
	    }

	    // Check to see if the problem can be split in two.
	    String[] hm = diff_halfMatch(text1, text2);
	    if (hm != null) {
	      // A half-match was found, sort out the return data.
	      String text1_a = hm[0];
	      String text1_b = hm[1];
	      String text2_a = hm[2];
	      String text2_b = hm[3];
	      String mid_common = hm[4];
	      // Send both pairs off for separate processing.
	      LinkedList<Diff> diffs_a = diff_main(text1_a, text2_a,
	                                           checklines, deadline);
	      LinkedList<Diff> diffs_b = diff_main(text1_b, text2_b,
	                                           checklines, deadline);
	      // Merge the results.
	      diffs = diffs_a;
	      diffs.add(new Diff(Operation.EQUAL, mid_common));
	      diffs.addAll(diffs_b);
	      return diffs;
	    }

	    if (checklines && text1.length() > 100 && text2.length() > 100) {
	      return diff_lineMode(text1, text2, deadline);
	    }

	    return diff_bisect(text1, text2, deadline);
	  }

	  /**
	   * Do a quick line-level diff on both strings, then rediff the parts for
	   * greater accuracy.
	   * This speedup can produce non-minimal diffs.
	   * @param text1 Old string to be diffed.
	   * @param text2 New string to be diffed.
	   * @param deadline Time when the diff should be complete by.
	   * @return Linked List of Diff objects.
	   */
	  private LinkedList<Diff> diff_lineMode(String text1, String text2,
	                                         long deadline) {
	    // Scan the text on a line-by-line basis first.
	    LinesToCharsResult b = diff_linesToChars(text1, text2);
	    text1 = b.chars1;
	    text2 = b.chars2;
	    List<String> linearray = b.lineArray;

	    LinkedList<Diff> diffs = diff_main(text1, text2, false, deadline);

	    // Convert the diff back to original text.
	    diff_charsToLines(diffs, linearray);
	    // Eliminate freak matches (e.g. blank lines)
	    diff_cleanupSemantic(diffs);

	    // Rediff any replacement blocks, this time character-by-character.
	    // Add a dummy entry at the end.
	    diffs.add(new Diff(Operation.EQUAL, ""));
	    int count_delete = 0;
	    int count_insert = 0;
	    String text_delete = "";
	    String text_insert = "";
	    ListIterator<Diff> pointer = diffs.listIterator();
	    Diff thisDiff = pointer.next();
	    while (thisDiff != null) {
	      switch (thisDiff.operation) {
	      case INSERT:
	        count_insert++;
	        text_insert += thisDiff.text;
	        break;
	      case DELETE:
	        count_delete++;
	        text_delete += thisDiff.text;
	        break;
	      case EQUAL:
	        // Upon reaching an equality, check for prior redundancies.
	        if (count_delete >= 1 && count_insert >= 1) {
	          // Delete the offending records and add the merged ones.
	          pointer.previous();
	          for (int j = 0; j < count_delete + count_insert; j++) {
	            pointer.previous();
	            pointer.remove();
	          }
	          for (Diff newDiff : diff_main(text_delete, text_insert, false,
	              deadline)) {
	            pointer.add(newDiff);
	          }
	        }
	        count_insert = 0;
	        count_delete = 0;
	        text_delete = "";
	        text_insert = "";
	        break;
	      }
	      thisDiff = pointer.hasNext() ? pointer.next() : null;
	    }
	    diffs.removeLast();  // Remove the dummy entry at the end.

	    return diffs;
	  }

	  /**
	   * Find the 'middle snake' of a diff, split the problem in two
	   * and return the recursively constructed diff.
	   * See Myers 1986 paper: An O(ND) Difference Algorithm and Its Variations.
	   * @param text1 Old string to be diffed.
	   * @param text2 New string to be diffed.
	   * @param deadline Time at which to bail if not yet complete.
	   * @return LinkedList of Diff objects.
	   */
	  protected LinkedList<Diff> diff_bisect(String text1, String text2,
	      long deadline) {
	    // Cache the text lengths to prevent multiple calls.
	    int text1_length = text1.length();
	    int text2_length = text2.length();
	    int max_d = (text1_length + text2_length + 1) / 2;
	    int v_offset = max_d;
	    int v_length = 2 * max_d;
	    int[] v1 = new int[v_length];
	    int[] v2 = new int[v_length];
	    for (int x = 0; x < v_length; x++) {
	      v1[x] = -1;
	      v2[x] = -1;
	    }
	    v1[v_offset + 1] = 0;
	    v2[v_offset + 1] = 0;
	    int delta = text1_length - text2_length;
	    // If the total number of characters is odd, then the front path will
	    // collide with the reverse path.
	    boolean front = (delta % 2 != 0);
	    // Offsets for start and end of k loop.
	    // Prevents mapping of space beyond the grid.
	    int k1start = 0;
	    int k1end = 0;
	    int k2start = 0;
	    int k2end = 0;
	    for (int d = 0; d < max_d; d++) {
	      // Bail out if deadline is reached.
	      if (System.currentTimeMillis() > deadline) {
	        break;
	      }

	      // Walk the front path one step.
	      for (int k1 = -d + k1start; k1 <= d - k1end; k1 += 2) {
	        int k1_offset = v_offset + k1;
	        int x1;
	        if (k1 == -d || (k1 != d && v1[k1_offset - 1] < v1[k1_offset + 1])) {
	          x1 = v1[k1_offset + 1];
	        } else {
	          x1 = v1[k1_offset - 1] + 1;
	        }
	        int y1 = x1 - k1;
	        while (x1 < text1_length && y1 < text2_length
	               && text1.charAt(x1) == text2.charAt(y1)) {
	          x1++;
	          y1++;
	        }
	        v1[k1_offset] = x1;
	        if (x1 > text1_length) {
	          // Ran off the right of the graph.
	          k1end += 2;
	        } else if (y1 > text2_length) {
	          // Ran off the bottom of the graph.
	          k1start += 2;
	        } else if (front) {
	          int k2_offset = v_offset + delta - k1;
	          if (k2_offset >= 0 && k2_offset < v_length && v2[k2_offset] != -1) {
	            // Mirror x2 onto top-left coordinate system.
	            int x2 = text1_length - v2[k2_offset];
	            if (x1 >= x2) {
	              // Overlap detected.
	              return diff_bisectSplit(text1, text2, x1, y1, deadline);
	            }
	          }
	        }
	      }

	      // Walk the reverse path one step.
	      for (int k2 = -d + k2start; k2 <= d - k2end; k2 += 2) {
	        int k2_offset = v_offset + k2;
	        int x2;
	        if (k2 == -d || (k2 != d && v2[k2_offset - 1] < v2[k2_offset + 1])) {
	          x2 = v2[k2_offset + 1];
	        } else {
	          x2 = v2[k2_offset - 1] + 1;
	        }
	        int y2 = x2 - k2;
	        while (x2 < text1_length && y2 < text2_length
	               && text1.charAt(text1_length - x2 - 1)
	               == text2.charAt(text2_length - y2 - 1)) {
	          x2++;
	          y2++;
	        }
	        v2[k2_offset] = x2;
	        if (x2 > text1_length) {
	          // Ran off the left of the graph.
	          k2end += 2;
	        } else if (y2 > text2_length) {
	          // Ran off the top of the graph.
	          k2start += 2;
	        } else if (!front) {
	          int k1_offset = v_offset + delta - k2;
	          if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] != -1) {
	            int x1 = v1[k1_offset];
	            int y1 = v_offset + x1 - k1_offset;
	            // Mirror x2 onto top-left coordinate system.
	            x2 = text1_length - x2;
	            if (x1 >= x2) {
	              // Overlap detected.
	              return diff_bisectSplit(text1, text2, x1, y1, deadline);
	            }
	          }
	        }
	      }
	    }
	    // Diff took too long and hit the deadline or
	    // number of diffs equals number of characters, no commonality at all.
	    LinkedList<Diff> diffs = new LinkedList<Diff>();
	    diffs.add(new Diff(Operation.DELETE, text1));
	    diffs.add(new Diff(Operation.INSERT, text2));
	    return diffs;
	  }

	  /**
	   * Given the location of the 'middle snake', split the diff in two parts
	   * and recurse.
	   * @param text1 Old string to be diffed.
	   * @param text2 New string to be diffed.
	   * @param x Index of split point in text1.
	   * @param y Index of split point in text2.
	   * @param deadline Time at which to bail if not yet complete.
	   * @return LinkedList of Diff objects.
	   */
	  private LinkedList<Diff> diff_bisectSplit(String text1, String text2,
	                                            int x, int y, long deadline) {
	    String text1a = text1.substring(0, x);
	    String text2a = text2.substring(0, y);
	    String text1b = text1.substring(x);
	    String text2b = text2.substring(y);

	    // Compute both diffs serially.
	    LinkedList<Diff> diffs = diff_main(text1a, text2a, false, deadline);
	    LinkedList<Diff> diffsb = diff_main(text1b, text2b, false, deadline);

	    diffs.addAll(diffsb);
	    return diffs;
	  }

	  /**
	   * Split two texts into a list of strings.  Reduce the texts to a string of
	   * hashes where each Unicode character represents one line.
	   * @param text1 First string.
	   * @param text2 Second string.
	   * @return An object containing the encoded text1, the encoded text2 and
	   *     the List of unique strings.  The zeroth element of the List of
	   *     unique strings is intentionally blank.
	   */
	  protected LinesToCharsResult diff_linesToChars(String text1, String text2) {
	    List<String> lineArray = new ArrayList<String>();
	    Map<String, Integer> lineHash = new HashMap<String, Integer>();
	    // e.g. linearray[4] == "Hello\n"
	    // e.g. linehash.get("Hello\n") == 4

	    // "\x00" is a valid character, but various debuggers don't like it.
	    // So we'll insert a junk entry to avoid generating a null character.
	    lineArray.add("");

	    String chars1 = diff_linesToCharsMunge(text1, lineArray, lineHash);
	    String chars2 = diff_linesToCharsMunge(text2, lineArray, lineHash);
	    return new LinesToCharsResult(chars1, chars2, lineArray);
	  }

	  /**
	   * Split a text into a list of strings.  Reduce the texts to a string of
	   * hashes where each Unicode character represents one line.
	   * @param text String to encode.
	   * @param lineArray List of unique strings.
	   * @param lineHash Map of strings to indices.
	   * @return Encoded string.
	   */
	  private String diff_linesToCharsMunge(String text, List<String> lineArray,
	                                        Map<String, Integer> lineHash) {
	    int lineStart = 0;
	    int lineEnd = -1;
	    String line;
	    StringBuilder chars = new StringBuilder();
	    // Walk the text, pulling out a substring for each line.
	    // text.split('\n') would would temporarily double our memory footprint.
	    // Modifying text would create many large strings to garbage collect.
	    while (lineEnd < text.length() - 1) {
	      lineEnd = text.indexOf('\n', lineStart);
	      if (lineEnd == -1) {
	        lineEnd = text.length() - 1;
	      }
	      line = text.substring(lineStart, lineEnd + 1);
	      lineStart = lineEnd + 1;

	      if (lineHash.containsKey(line)) {
	        chars.append(String.valueOf((char) (int) lineHash.get(line)));
	      } else {
	        lineArray.add(line);
	        lineHash.put(line, lineArray.size() - 1);
	        chars.append(String.valueOf((char) (lineArray.size() - 1)));
	      }
	    }
	    return chars.toString();
	  }

	  /**
	   * Rehydrate the text in a diff from a string of line hashes to real lines of
	   * text.
	   * @param diffs LinkedList of Diff objects.
	   * @param lineArray List of unique strings.
	   */
	  protected void diff_charsToLines(LinkedList<Diff> diffs,
	                                  List<String> lineArray) {
	    StringBuilder text;
	    for (Diff diff : diffs) {
	      text = new StringBuilder();
	      for (int y = 0; y < diff.text.length(); y++) {
	        text.append(lineArray.get(diff.text.charAt(y)));
	      }
	      diff.text = text.toString();
	    }
	  }

	  /**
	   * Determine the common prefix of two strings
	   * @param text1 First string.
	   * @param text2 Second string.
	   * @return The number of characters common to the start of each string.
	   */
	  public int diff_commonPrefix(String text1, String text2) {
	    // Performance analysis: http://neil.fraser.name/news/2007/10/09/
	    int n = Math.min(text1.length(), text2.length());
	    for (int i = 0; i < n; i++) {
	      if (text1.charAt(i) != text2.charAt(i)) {
	        return i;
	      }
	    }
	    return n;
	  }

	  /**
	   * Determine the common suffix of two strings
	   * @param text1 First string.
	   * @param text2 Second string.
	   * @return The number of characters common to the end of each string.
	   */
	  public int diff_commonSuffix(String text1, String text2) {
	    // Performance analysis: http://neil.fraser.name/news/2007/10/09/
	    int text1_length = text1.length();
	    int text2_length = text2.length();
	    int n = Math.min(text1_length, text2_length);
	    for (int i = 1; i <= n; i++) {
	      if (text1.charAt(text1_length - i) != text2.charAt(text2_length - i)) {
	        return i - 1;
	      }
	    }
	    return n;
	  }

	  /**
	   * Determine if the suffix of one string is the prefix of another.
	   * @param text1 First string.
	   * @param text2 Second string.
	   * @return The number of characters common to the end of the first
	   *     string and the start of the second string.
	   */
	  protected int diff_commonOverlap(String text1, String text2) {
	    // Cache the text lengths to prevent multiple calls.
	    int text1_length = text1.length();
	    int text2_length = text2.length();
	    // Eliminate the null case.
	    if (text1_length == 0 || text2_length == 0) {
	      return 0;
	    }
	    // Truncate the longer string.
	    if (text1_length > text2_length) {
	      text1 = text1.substring(text1_length - text2_length);
	    } else if (text1_length < text2_length) {
	      text2 = text2.substring(0, text1_length);
	    }
	    int text_length = Math.min(text1_length, text2_length);
	    // Quick check for the worst case.
	    if (text1.equals(text2)) {
	      return text_length;
	    }

	    // Start by looking for a single character match
	    // and increase length until no match is found.
	    // Performance analysis: http://neil.fraser.name/news/2010/11/04/
	    int best = 0;
	    int length = 1;
	    while (true) {
	      String pattern = text1.substring(text_length - length);
	      int found = text2.indexOf(pattern);
	      if (found == -1) {
	        return best;
	      }
	      length += found;
	      if (found == 0 || text1.substring(text_length - length).equals(
	          text2.substring(0, length))) {
	        best = length;
	        length++;
	      }
	    }
	  }

	  /**
	   * Do the two texts share a substring which is at least half the length of
	   * the longer text?
	   * This speedup can produce non-minimal diffs.
	   * @param text1 First string.
	   * @param text2 Second string.
	   * @return Five element String array, containing the prefix of text1, the
	   *     suffix of text1, the prefix of text2, the suffix of text2 and the
	   *     common middle.  Or null if there was no match.
	   */
	  protected String[] diff_halfMatch(String text1, String text2) {
	    if (Diff_Timeout <= 0) {
	      // Don't risk returning a non-optimal diff if we have unlimited time.
	      return null;
	    }
	    String longtext = text1.length() > text2.length() ? text1 : text2;
	    String shorttext = text1.length() > text2.length() ? text2 : text1;
	    if (longtext.length() < 4 || shorttext.length() * 2 < longtext.length()) {
	      return null;  // Pointless.
	    }

	    // First check if the second quarter is the seed for a half-match.
	    String[] hm1 = diff_halfMatchI(longtext, shorttext,
	                                   (longtext.length() + 3) / 4);
	    // Check again based on the third quarter.
	    String[] hm2 = diff_halfMatchI(longtext, shorttext,
	                                   (longtext.length() + 1) / 2);
	    String[] hm;
	    if (hm1 == null && hm2 == null) {
	      return null;
	    } else if (hm2 == null) {
	      hm = hm1;
	    } else if (hm1 == null) {
	      hm = hm2;
	    } else {
	      // Both matched.  Select the longest.
	      hm = hm1[4].length() > hm2[4].length() ? hm1 : hm2;
	    }

	    // A half-match was found, sort out the return data.
	    if (text1.length() > text2.length()) {
	      return hm;
	      //return new String[]{hm[0], hm[1], hm[2], hm[3], hm[4]};
	    } else {
	      return new String[]{hm[2], hm[3], hm[0], hm[1], hm[4]};
	    }
	  }

	  /**
	   * Does a substring of shorttext exist within longtext such that the
	   * substring is at least half the length of longtext?
	   * @param longtext Longer string.
	   * @param shorttext Shorter string.
	   * @param i Start index of quarter length substring within longtext.
	   * @return Five element String array, containing the prefix of longtext, the
	   *     suffix of longtext, the prefix of shorttext, the suffix of shorttext
	   *     and the common middle.  Or null if there was no match.
	   */
	  private String[] diff_halfMatchI(String longtext, String shorttext, int i) {
	    // Start with a 1/4 length substring at position i as a seed.
	    String seed = longtext.substring(i, i + longtext.length() / 4);
	    int j = -1;
	    String best_common = "";
	    String best_longtext_a = "", best_longtext_b = "";
	    String best_shorttext_a = "", best_shorttext_b = "";
	    while ((j = shorttext.indexOf(seed, j + 1)) != -1) {
	      int prefixLength = diff_commonPrefix(longtext.substring(i),
	                                           shorttext.substring(j));
	      int suffixLength = diff_commonSuffix(longtext.substring(0, i),
	                                           shorttext.substring(0, j));
	      if (best_common.length() < suffixLength + prefixLength) {
	        best_common = shorttext.substring(j - suffixLength, j)
	            + shorttext.substring(j, j + prefixLength);
	        best_longtext_a = longtext.substring(0, i - suffixLength);
	        best_longtext_b = longtext.substring(i + prefixLength);
	        best_shorttext_a = shorttext.substring(0, j - suffixLength);
	        best_shorttext_b = shorttext.substring(j + prefixLength);
	      }
	    }
	    if (best_common.length() * 2 >= longtext.length()) {
	      return new String[]{best_longtext_a, best_longtext_b,
	                          best_shorttext_a, best_shorttext_b, best_common};
	    } else {
	      return null;
	    }
	  }

	  /**
	   * Reduce the number of edits by eliminating semantically trivial equalities.
	   * @param diffs LinkedList of Diff objects.
	   */
	  public void diff_cleanupSemantic(LinkedList<Diff> diffs) {
	    if (diffs.isEmpty()) {
	      return;
	    }
	    boolean changes = false;
	    Stack<Diff> equalities = new Stack<Diff>();  // Stack of qualities.
	    String lastequality = null; // Always equal to equalities.lastElement().text
	    ListIterator<Diff> pointer = diffs.listIterator();
	    // Number of characters that changed prior to the equality.
	    int length_insertions1 = 0;
	    int length_deletions1 = 0;
	    // Number of characters that changed after the equality.
	    int length_insertions2 = 0;
	    int length_deletions2 = 0;
	    Diff thisDiff = pointer.next();
	    while (thisDiff != null) {
	      if (thisDiff.operation == Operation.EQUAL) {
	        // Equality found.
	        equalities.push(thisDiff);
	        length_insertions1 = length_insertions2;
	        length_deletions1 = length_deletions2;
	        length_insertions2 = 0;
	        length_deletions2 = 0;
	        lastequality = thisDiff.text;
	      } else {
	        // An insertion or deletion.
	        if (thisDiff.operation == Operation.INSERT) {
	          length_insertions2 += thisDiff.text.length();
	        } else {
	          length_deletions2 += thisDiff.text.length();
	        }
	        // Eliminate an equality that is smaller or equal to the edits on both
	        // sides of it.
	        if (lastequality != null && (lastequality.length()
	            <= Math.max(length_insertions1, length_deletions1))
	            && (lastequality.length()
	                <= Math.max(length_insertions2, length_deletions2))) {
	          //System.out.println("Splitting: '" + lastequality + "'");
	          // Walk back to offending equality.
	          while (thisDiff != equalities.lastElement()) {
	            thisDiff = pointer.previous();
	          }
	          pointer.next();

	          // Replace equality with a delete.
	          pointer.set(new Diff(Operation.DELETE, lastequality));
	          // Insert a corresponding an insert.
	          pointer.add(new Diff(Operation.INSERT, lastequality));

	          equalities.pop();  // Throw away the equality we just deleted.
	          if (!equalities.empty()) {
	            // Throw away the previous equality (it needs to be reevaluated).
	            equalities.pop();
	          }
	          if (equalities.empty()) {
	            // There are no previous equalities, walk back to the start.
	            while (pointer.hasPrevious()) {
	              pointer.previous();
	            }
	          } else {
	            // There is a safe equality we can fall back to.
	            thisDiff = equalities.lastElement();
	            while (thisDiff != pointer.previous()) {
	              // Intentionally empty loop.
	            }
	          }

	          length_insertions1 = 0;  // Reset the counters.
	          length_insertions2 = 0;
	          length_deletions1 = 0;
	          length_deletions2 = 0;
	          lastequality = null;
	          changes = true;
	        }
	      }
	      thisDiff = pointer.hasNext() ? pointer.next() : null;
	    }

	    // Normalize the diff.
	    if (changes) {
	      diff_cleanupMerge(diffs);
	    }
	    diff_cleanupSemanticLossless(diffs);

	    // Find any overlaps between deletions and insertions.
	    // e.g: <del>abcxxx</del><ins>xxxdef</ins>
	    //   -> <del>abc</del>xxx<ins>def</ins>
	    // e.g: <del>xxxabc</del><ins>defxxx</ins>
	    //   -> <ins>def</ins>xxx<del>abc</del>
	    // Only extract an overlap if it is as big as the edit ahead or behind it.
	    pointer = diffs.listIterator();
	    Diff prevDiff = null;
	    thisDiff = null;
	    if (pointer.hasNext()) {
	      prevDiff = pointer.next();
	      if (pointer.hasNext()) {
	        thisDiff = pointer.next();
	      }
	    }
	    while (thisDiff != null) {
	      if (prevDiff.operation == Operation.DELETE &&
	          thisDiff.operation == Operation.INSERT) {
	        String deletion = prevDiff.text;
	        String insertion = thisDiff.text;
	        int overlap_length1 = this.diff_commonOverlap(deletion, insertion);
	        int overlap_length2 = this.diff_commonOverlap(insertion, deletion);
	        if (overlap_length1 >= overlap_length2) {
	          if (overlap_length1 >= deletion.length() / 2.0 ||
	              overlap_length1 >= insertion.length() / 2.0) {
	            // Overlap found. Insert an equality and trim the surrounding edits.
	            pointer.previous();
	            pointer.add(new Diff(Operation.EQUAL,
	                                 insertion.substring(0, overlap_length1)));
	            prevDiff.text =
	                deletion.substring(0, deletion.length() - overlap_length1);
	            thisDiff.text = insertion.substring(overlap_length1);
	            // pointer.add inserts the element before the cursor, so there is
	            // no need to step past the new element.
	          }
	        } else {
	          if (overlap_length2 >= deletion.length() / 2.0 ||
	              overlap_length2 >= insertion.length() / 2.0) {
	            // Reverse overlap found.
	            // Insert an equality and swap and trim the surrounding edits.
	            pointer.previous();
	            pointer.add(new Diff(Operation.EQUAL,
	                                 deletion.substring(0, overlap_length2)));
	            prevDiff.operation = Operation.INSERT;
	            prevDiff.text =
	              insertion.substring(0, insertion.length() - overlap_length2);
	            thisDiff.operation = Operation.DELETE;
	            thisDiff.text = deletion.substring(overlap_length2);
	            // pointer.add inserts the element before the cursor, so there is
	            // no need to step past the new element.
	          }
	        }
	        thisDiff = pointer.hasNext() ? pointer.next() : null;
	      }
	      prevDiff = thisDiff;
	      thisDiff = pointer.hasNext() ? pointer.next() : null;
	    }
	  }

	  /**
	   * Look for single edits surrounded on both sides by equalities
	   * which can be shifted sideways to align the edit to a word boundary.
	   * e.g: The c<ins>at c</ins>ame. -> The <ins>cat </ins>came.
	   * @param diffs LinkedList of Diff objects.
	   */
	  public void diff_cleanupSemanticLossless(LinkedList<Diff> diffs) {
	    String equality1, edit, equality2;
	    String commonString;
	    int commonOffset;
	    int score, bestScore;
	    String bestEquality1, bestEdit, bestEquality2;
	    // Create a new iterator at the start.
	    ListIterator<Diff> pointer = diffs.listIterator();
	    Diff prevDiff = pointer.hasNext() ? pointer.next() : null;
	    Diff thisDiff = pointer.hasNext() ? pointer.next() : null;
	    Diff nextDiff = pointer.hasNext() ? pointer.next() : null;
	    // Intentionally ignore the first and last element (don't need checking).
	    while (nextDiff != null) {
	      if (prevDiff.operation == Operation.EQUAL &&
	          nextDiff.operation == Operation.EQUAL) {
	        // This is a single edit surrounded by equalities.
	        equality1 = prevDiff.text;
	        edit = thisDiff.text;
	        equality2 = nextDiff.text;

	        // First, shift the edit as far left as possible.
	        commonOffset = diff_commonSuffix(equality1, edit);
	        if (commonOffset != 0) {
	          commonString = edit.substring(edit.length() - commonOffset);
	          equality1 = equality1.substring(0, equality1.length() - commonOffset);
	          edit = commonString + edit.substring(0, edit.length() - commonOffset);
	          equality2 = commonString + equality2;
	        }

	        // Second, step character by character right, looking for the best fit.
	        bestEquality1 = equality1;
	        bestEdit = edit;
	        bestEquality2 = equality2;
	        bestScore = diff_cleanupSemanticScore(equality1, edit)
	            + diff_cleanupSemanticScore(edit, equality2);
	        while (edit.length() != 0 && equality2.length() != 0
	            && edit.charAt(0) == equality2.charAt(0)) {
	          equality1 += edit.charAt(0);
	          edit = edit.substring(1) + equality2.charAt(0);
	          equality2 = equality2.substring(1);
	          score = diff_cleanupSemanticScore(equality1, edit)
	              + diff_cleanupSemanticScore(edit, equality2);
	          // The >= encourages trailing rather than leading whitespace on edits.
	          if (score >= bestScore) {
	            bestScore = score;
	            bestEquality1 = equality1;
	            bestEdit = edit;
	            bestEquality2 = equality2;
	          }
	        }

	        if (!prevDiff.text.equals(bestEquality1)) {
	          // We have an improvement, save it back to the diff.
	          if (bestEquality1.length() != 0) {
	            prevDiff.text = bestEquality1;
	          } else {
	            pointer.previous(); // Walk past nextDiff.
	            pointer.previous(); // Walk past thisDiff.
	            pointer.previous(); // Walk past prevDiff.
	            pointer.remove(); // Delete prevDiff.
	            pointer.next(); // Walk past thisDiff.
	            pointer.next(); // Walk past nextDiff.
	          }
	          thisDiff.text = bestEdit;
	          if (bestEquality2.length() != 0) {
	            nextDiff.text = bestEquality2;
	          } else {
	            pointer.remove(); // Delete nextDiff.
	            nextDiff = thisDiff;
	            thisDiff = prevDiff;
	          }
	        }
	      }
	      prevDiff = thisDiff;
	      thisDiff = nextDiff;
	      nextDiff = pointer.hasNext() ? pointer.next() : null;
	    }
	  }

	  /**
	   * Given two strings, compute a score representing whether the internal
	   * boundary falls on logical boundaries.
	   * Scores range from 6 (best) to 0 (worst).
	   * @param one First string.
	   * @param two Second string.
	   * @return The score.
	   */
	  private int diff_cleanupSemanticScore(String one, String two) {
	    if (one.length() == 0 || two.length() == 0) {
	      // Edges are the best.
	      return 6;
	    }

	    // Each port of this function behaves slightly differently due to
	    // subtle differences in each language's definition of things like
	    // 'whitespace'.  Since this function's purpose is largely cosmetic,
	    // the choice has been made to use each language's native features
	    // rather than force total conformity.
	    char char1 = one.charAt(one.length() - 1);
	    char char2 = two.charAt(0);
	    boolean nonAlphaNumeric1 = !Character.isLetterOrDigit(char1);
	    boolean nonAlphaNumeric2 = !Character.isLetterOrDigit(char2);
	    boolean whitespace1 = nonAlphaNumeric1 && Character.isWhitespace(char1);
	    boolean whitespace2 = nonAlphaNumeric2 && Character.isWhitespace(char2);
	    boolean lineBreak1 = whitespace1
	        && Character.getType(char1) == Character.CONTROL;
	    boolean lineBreak2 = whitespace2
	        && Character.getType(char2) == Character.CONTROL;
	    boolean blankLine1 = lineBreak1 && BLANKLINEEND.matcher(one).find();
	    boolean blankLine2 = lineBreak2 && BLANKLINESTART.matcher(two).find();

	    if (blankLine1 || blankLine2) {
	      // Five points for blank lines.
	      return 5;
	    } else if (lineBreak1 || lineBreak2) {
	      // Four points for line breaks.
	      return 4;
	    } else if (nonAlphaNumeric1 && !whitespace1 && whitespace2) {
	      // Three points for end of sentences.
	      return 3;
	    } else if (whitespace1 || whitespace2) {
	      // Two points for whitespace.
	      return 2;
	    } else if (nonAlphaNumeric1 || nonAlphaNumeric2) {
	      // One point for non-alphanumeric.
	      return 1;
	    }
	    return 0;
	  }

	  // Define some regex patterns for matching boundaries.
	  private Pattern BLANKLINEEND
	      = Pattern.compile("\\n\\r?\\n\\Z", Pattern.DOTALL);
	  private Pattern BLANKLINESTART
	      = Pattern.compile("\\A\\r?\\n\\r?\\n", Pattern.DOTALL);

	  /**
	   * Reduce the number of edits by eliminating operationally trivial equalities.
	   * @param diffs LinkedList of Diff objects.
	   */
	  public void diff_cleanupEfficiency(LinkedList<Diff> diffs) {
	    if (diffs.isEmpty()) {
	      return;
	    }
	    boolean changes = false;
	    Stack<Diff> equalities = new Stack<Diff>();  // Stack of equalities.
	    String lastequality = null; // Always equal to equalities.lastElement().text
	    ListIterator<Diff> pointer = diffs.listIterator();
	    // Is there an insertion operation before the last equality.
	    boolean pre_ins = false;
	    // Is there a deletion operation before the last equality.
	    boolean pre_del = false;
	    // Is there an insertion operation after the last equality.
	    boolean post_ins = false;
	    // Is there a deletion operation after the last equality.
	    boolean post_del = false;
	    Diff thisDiff = pointer.next();
	    Diff safeDiff = thisDiff;  // The last Diff that is known to be unsplitable.
	    while (thisDiff != null) {
	      if (thisDiff.operation == Operation.EQUAL) {
	        // Equality found.
	        if (thisDiff.text.length() < Diff_EditCost && (post_ins || post_del)) {
	          // Candidate found.
	          equalities.push(thisDiff);
	          pre_ins = post_ins;
	          pre_del = post_del;
	          lastequality = thisDiff.text;
	        } else {
	          // Not a candidate, and can never become one.
	          equalities.clear();
	          lastequality = null;
	          safeDiff = thisDiff;
	        }
	        post_ins = post_del = false;
	      } else {
	        // An insertion or deletion.
	        if (thisDiff.operation == Operation.DELETE) {
	          post_del = true;
	        } else {
	          post_ins = true;
	        }
	        /*
	         * Five types to be split:
	         * <ins>A</ins><del>B</del>XY<ins>C</ins><del>D</del>
	         * <ins>A</ins>X<ins>C</ins><del>D</del>
	         * <ins>A</ins><del>B</del>X<ins>C</ins>
	         * <ins>A</del>X<ins>C</ins><del>D</del>
	         * <ins>A</ins><del>B</del>X<del>C</del>
	         */
	        if (lastequality != null
	            && ((pre_ins && pre_del && post_ins && post_del)
	                || ((lastequality.length() < Diff_EditCost / 2)
	                    && ((pre_ins ? 1 : 0) + (pre_del ? 1 : 0)
	                        + (post_ins ? 1 : 0) + (post_del ? 1 : 0)) == 3))) {
	          //System.out.println("Splitting: '" + lastequality + "'");
	          // Walk back to offending equality.
	          while (thisDiff != equalities.lastElement()) {
	            thisDiff = pointer.previous();
	          }
	          pointer.next();

	          // Replace equality with a delete.
	          pointer.set(new Diff(Operation.DELETE, lastequality));
	          // Insert a corresponding an insert.
	          pointer.add(thisDiff = new Diff(Operation.INSERT, lastequality));

	          equalities.pop();  // Throw away the equality we just deleted.
	          lastequality = null;
	          if (pre_ins && pre_del) {
	            // No changes made which could affect previous entry, keep going.
	            post_ins = post_del = true;
	            equalities.clear();
	            safeDiff = thisDiff;
	          } else {
	            if (!equalities.empty()) {
	              // Throw away the previous equality (it needs to be reevaluated).
	              equalities.pop();
	            }
	            if (equalities.empty()) {
	              // There are no previous questionable equalities,
	              // walk back to the last known safe diff.
	              thisDiff = safeDiff;
	            } else {
	              // There is an equality we can fall back to.
	              thisDiff = equalities.lastElement();
	            }
	            while (thisDiff != pointer.previous()) {
	              // Intentionally empty loop.
	            }
	            post_ins = post_del = false;
	          }

	          changes = true;
	        }
	      }
	      thisDiff = pointer.hasNext() ? pointer.next() : null;
	    }

	    if (changes) {
	      diff_cleanupMerge(diffs);
	    }
	  }

	  /**
	   * Reorder and merge like edit sections.  Merge equalities.
	   * Any edit section can move as long as it doesn't cross an equality.
	   * @param diffs LinkedList of Diff objects.
	   */
	  public void diff_cleanupMerge(LinkedList<Diff> diffs) {
	    diffs.add(new Diff(Operation.EQUAL, ""));  // Add a dummy entry at the end.
	    ListIterator<Diff> pointer = diffs.listIterator();
	    int count_delete = 0;
	    int count_insert = 0;
	    String text_delete = "";
	    String text_insert = "";
	    Diff thisDiff = pointer.next();
	    Diff prevEqual = null;
	    int commonlength;
	    while (thisDiff != null) {
	      switch (thisDiff.operation) {
	      case INSERT:
	        count_insert++;
	        text_insert += thisDiff.text;
	        prevEqual = null;
	        break;
	      case DELETE:
	        count_delete++;
	        text_delete += thisDiff.text;
	        prevEqual = null;
	        break;
	      case EQUAL:
	        if (count_delete + count_insert > 1) {
	          boolean both_types = count_delete != 0 && count_insert != 0;
	          // Delete the offending records.
	          pointer.previous();  // Reverse direction.
	          while (count_delete-- > 0) {
	            pointer.previous();
	            pointer.remove();
	          }
	          while (count_insert-- > 0) {
	            pointer.previous();
	            pointer.remove();
	          }
	          if (both_types) {
	            // Factor out any common prefixies.
	            commonlength = diff_commonPrefix(text_insert, text_delete);
	            if (commonlength != 0) {
	              if (pointer.hasPrevious()) {
	                thisDiff = pointer.previous();
	                assert thisDiff.operation == Operation.EQUAL
	                       : "Previous diff should have been an equality.";
	                thisDiff.text += text_insert.substring(0, commonlength);
	                pointer.next();
	              } else {
	                pointer.add(new Diff(Operation.EQUAL,
	                    text_insert.substring(0, commonlength)));
	              }
	              text_insert = text_insert.substring(commonlength);
	              text_delete = text_delete.substring(commonlength);
	            }
	            // Factor out any common suffixies.
	            commonlength = diff_commonSuffix(text_insert, text_delete);
	            if (commonlength != 0) {
	              thisDiff = pointer.next();
	              thisDiff.text = text_insert.substring(text_insert.length()
	                  - commonlength) + thisDiff.text;
	              text_insert = text_insert.substring(0, text_insert.length()
	                  - commonlength);
	              text_delete = text_delete.substring(0, text_delete.length()
	                  - commonlength);
	              pointer.previous();
	            }
	          }
	          // Insert the merged records.
	          if (text_delete.length() != 0) {
	            pointer.add(new Diff(Operation.DELETE, text_delete));
	          }
	          if (text_insert.length() != 0) {
	            pointer.add(new Diff(Operation.INSERT, text_insert));
	          }
	          // Step forward to the equality.
	          thisDiff = pointer.hasNext() ? pointer.next() : null;
	        } else if (prevEqual != null) {
	          // Merge this equality with the previous one.
	          prevEqual.text += thisDiff.text;
	          pointer.remove();
	          thisDiff = pointer.previous();
	          pointer.next();  // Forward direction
	        }
	        count_insert = 0;
	        count_delete = 0;
	        text_delete = "";
	        text_insert = "";
	        prevEqual = thisDiff;
	        break;
	      }
	      thisDiff = pointer.hasNext() ? pointer.next() : null;
	    }
	    if (diffs.getLast().text.length() == 0) {
	      diffs.removeLast();  // Remove the dummy entry at the end.
	    }

	    /*
	     * Second pass: look for single edits surrounded on both sides by equalities
	     * which can be shifted sideways to eliminate an equality.
	     * e.g: A<ins>BA</ins>C -> <ins>AB</ins>AC
	     */
	    boolean changes = false;
	    // Create a new iterator at the start.
	    // (As opposed to walking the current one back.)
	    pointer = diffs.listIterator();
	    Diff prevDiff = pointer.hasNext() ? pointer.next() : null;
	    thisDiff = pointer.hasNext() ? pointer.next() : null;
	    Diff nextDiff = pointer.hasNext() ? pointer.next() : null;
	    // Intentionally ignore the first and last element (don't need checking).
	    while (nextDiff != null) {
	      if (prevDiff.operation == Operation.EQUAL &&
	          nextDiff.operation == Operation.EQUAL) {
	        // This is a single edit surrounded by equalities.
	        if (thisDiff.text.endsWith(prevDiff.text)) {
	          // Shift the edit over the previous equality.
	          thisDiff.text = prevDiff.text
	              + thisDiff.text.substring(0, thisDiff.text.length()
	                                           - prevDiff.text.length());
	          nextDiff.text = prevDiff.text + nextDiff.text;
	          pointer.previous(); // Walk past nextDiff.
	          pointer.previous(); // Walk past thisDiff.
	          pointer.previous(); // Walk past prevDiff.
	          pointer.remove(); // Delete prevDiff.
	          pointer.next(); // Walk past thisDiff.
	          thisDiff = pointer.next(); // Walk past nextDiff.
	          nextDiff = pointer.hasNext() ? pointer.next() : null;
	          changes = true;
	        } else if (thisDiff.text.startsWith(nextDiff.text)) {
	          // Shift the edit over the next equality.
	          prevDiff.text += nextDiff.text;
	          thisDiff.text = thisDiff.text.substring(nextDiff.text.length())
	              + nextDiff.text;
	          pointer.remove(); // Delete nextDiff.
	          nextDiff = pointer.hasNext() ? pointer.next() : null;
	          changes = true;
	        }
	      }
	      prevDiff = thisDiff;
	      thisDiff = nextDiff;
	      nextDiff = pointer.hasNext() ? pointer.next() : null;
	    }
	    // If shifts were made, the diff needs reordering and another shift sweep.
	    if (changes) {
	      diff_cleanupMerge(diffs);
	    }
	  }

	  /**
	   * loc is a location in text1, compute and return the equivalent location in
	   * text2.
	   * e.g. "The cat" vs "The big cat", 1->1, 5->8
	   * @param diffs LinkedList of Diff objects.
	   * @param loc Location within text1.
	   * @return Location within text2.
	   */
	  public int diff_xIndex(LinkedList<Diff> diffs, int loc) {
	    int chars1 = 0;
	    int chars2 = 0;
	    int last_chars1 = 0;
	    int last_chars2 = 0;
	    Diff lastDiff = null;
	    for (Diff aDiff : diffs) {
	      if (aDiff.operation != Operation.INSERT) {
	        // Equality or deletion.
	        chars1 += aDiff.text.length();
	      }
	      if (aDiff.operation != Operation.DELETE) {
	        // Equality or insertion.
	        chars2 += aDiff.text.length();
	      }
	      if (chars1 > loc) {
	        // Overshot the location.
	        lastDiff = aDiff;
	        break;
	      }
	      last_chars1 = chars1;
	      last_chars2 = chars2;
	    }
	    if (lastDiff != null && lastDiff.operation == Operation.DELETE) {
	      // The location was deleted.
	      return last_chars2;
	    }
	    // Add the remaining character length.
	    return last_chars2 + (loc - last_chars1);
	  }

	  /**
	   * Convert a Diff list into a pretty HTML report.
	   * @param diffs LinkedList of Diff objects.
	   * @return HTML representation.
	   */
	  public String diff_prettyHtml(LinkedList<Diff> diffs) {
	    StringBuilder html = new StringBuilder();
	    for (Diff aDiff : diffs) {
	      String text = aDiff.text.replace("&", "&amp;").replace("<", "&lt;")
	          .replace(">", "&gt;").replace("\n", "&para;<br>");
	      switch (aDiff.operation) {
	      case INSERT:
	        html.append("<ins style=\"background:#e6ffe6;\">").append(text)
	            .append("</ins>");
	        break;
	      case DELETE:
	        html.append("<del style=\"background:#ffe6e6;\">").append(text)
	            .append("</del>");
	        break;
	      case EQUAL:
	        html.append("<span>").append(text).append("</span>");
	        break;
	      }
	    }
	    return html.toString();
	  }

	  /**
	   * Compute and return the source text (all equalities and deletions).
	   * @param diffs LinkedList of Diff objects.
	   * @return Source text.
	   */
	  public String diff_text1(LinkedList<Diff> diffs) {
	    StringBuilder text = new StringBuilder();
	    for (Diff aDiff : diffs) {
	      if (aDiff.operation != Operation.INSERT) {
	        text.append(aDiff.text);
	      }
	    }
	    return text.toString();
	  }

	  /**
	   * Compute and return the destination text (all equalities and insertions).
	   * @param diffs LinkedList of Diff objects.
	   * @return Destination text.
	   */
	  public String diff_text2(LinkedList<Diff> diffs) {
	    StringBuilder text = new StringBuilder();
	    for (Diff aDiff : diffs) {
	      if (aDiff.operation != Operation.DELETE) {
	        text.append(aDiff.text);
	      }
	    }
	    return text.toString();
	  }

	  /**
	   * Compute the Levenshtein distance; the number of inserted, deleted or
	   * substituted characters.
	   * @param diffs LinkedList of Diff objects.
	   * @return Number of changes.
	   */
	  public int diff_levenshtein(LinkedList<Diff> diffs) {
	    int levenshtein = 0;
	    int insertions = 0;
	    int deletions = 0;
	    for (Diff aDiff : diffs) {
	      switch (aDiff.operation) {
	      case INSERT:
	        insertions += aDiff.text.length();
	        break;
	      case DELETE:
	        deletions += aDiff.text.length();
	        break;
	      case EQUAL:
	        // A deletion and an insertion is one substitution.
	        levenshtein += Math.max(insertions, deletions);
	        insertions = 0;
	        deletions = 0;
	        break;
	      }
	    }
	    levenshtein += Math.max(insertions, deletions);
	    return levenshtein;
	  }

	  /**
	   * Crush the diff into an encoded string which describes the operations
	   * required to transform text1 into text2.
	   * E.g. =3\t-2\t+ing  -> Keep 3 chars, delete 2 chars, insert 'ing'.
	   * Operations are tab-separated.  Inserted text is escaped using %xx notation.
	   * @param diffs Array of Diff objects.
	   * @return Delta text.
	   */
	  public String diff_toDelta(LinkedList<Diff> diffs) {
	    StringBuilder text = new StringBuilder();
	    for (Diff aDiff : diffs) {
	      switch (aDiff.operation) {
	      case INSERT:
	        try {
	          text.append("+").append(URLEncoder.encode(aDiff.text, "UTF-8")
	                                            .replace('+', ' ')).append("\t");
	        } catch (UnsupportedEncodingException e) {
	          // Not likely on modern system.
	          throw new Error("This system does not support UTF-8.", e);
	        }
	        break;
	      case DELETE:
	        text.append("-").append(aDiff.text.length()).append("\t");
	        break;
	      case EQUAL:
	        text.append("=").append(aDiff.text.length()).append("\t");
	        break;
	      }
	    }
	    String delta = text.toString();
	    if (delta.length() != 0) {
	      // Strip off trailing tab character.
	      delta = delta.substring(0, delta.length() - 1);
	      delta = unescapeForEncodeUriCompatability(delta);
	    }
	    return delta;
	  }

	  /**
	   * Given the original text1, and an encoded string which describes the
	   * operations required to transform text1 into text2, compute the full diff.
	   * @param text1 Source string for the diff.
	   * @param delta Delta text.
	   * @return Array of Diff objects or null if invalid.
	   * @throws IllegalArgumentException If invalid input.
	   */
	  public LinkedList<Diff> diff_fromDelta(String text1, String delta)
	      throws IllegalArgumentException {
	    LinkedList<Diff> diffs = new LinkedList<Diff>();
	    int pointer = 0;  // Cursor in text1
	    String[] tokens = delta.split("\t");
	    for (String token : tokens) {
	      if (token.length() == 0) {
	        // Blank tokens are ok (from a trailing \t).
	        continue;
	      }
	      // Each token begins with a one character parameter which specifies the
	      // operation of this token (delete, insert, equality).
	      String param = token.substring(1);
	      switch (token.charAt(0)) {
	      case '+':
	        // decode would change all "+" to " "
	        param = param.replace("+", "%2B");
	        try {
	          param = URLDecoder.decode(param, "UTF-8");
	        } catch (UnsupportedEncodingException e) {
	          // Not likely on modern system.
	          throw new Error("This system does not support UTF-8.", e);
	        } catch (IllegalArgumentException e) {
	          // Malformed URI sequence.
	          throw new IllegalArgumentException(
	              "Illegal escape in diff_fromDelta: " + param, e);
	        }
	        diffs.add(new Diff(Operation.INSERT, param));
	        break;
	      case '-':
	        // Fall through.
	      case '=':
	        int n;
	        try {
	          n = Integer.parseInt(param);
	        } catch (NumberFormatException e) {
	          throw new IllegalArgumentException(
	              "Invalid number in diff_fromDelta: " + param, e);
	        }
	        if (n < 0) {
	          throw new IllegalArgumentException(
	              "Negative number in diff_fromDelta: " + param);
	        }
	        String text;
	        try {
	          text = text1.substring(pointer, pointer += n);
	        } catch (StringIndexOutOfBoundsException e) {
	          throw new IllegalArgumentException("Delta length (" + pointer
	              + ") larger than source text length (" + text1.length()
	              + ").", e);
	        }
	        if (token.charAt(0) == '=') {
	          diffs.add(new Diff(Operation.EQUAL, text));
	        } else {
	          diffs.add(new Diff(Operation.DELETE, text));
	        }
	        break;
	      default:
	        // Anything else is an error.
	        throw new IllegalArgumentException(
	            "Invalid diff operation in diff_fromDelta: " + token.charAt(0));
	      }
	    }
	    if (pointer != text1.length()) {
	      throw new IllegalArgumentException("Delta length (" + pointer
	          + ") smaller than source text length (" + text1.length() + ").");
	    }
	    return diffs;
	  }


	  //  MATCH FUNCTIONS


	  /**
	   * Locate the best instance of 'pattern' in 'text' near 'loc'.
	   * Returns -1 if no match found.
	   * @param text The text to search.
	   * @param pattern The pattern to search for.
	   * @param loc The location to search around.
	   * @return Best match index or -1.
	   */
	  public int match_main(String text, String pattern, int loc) {
	    // Check for null inputs.
	    if (text == null || pattern == null) {
	      throw new IllegalArgumentException("Null inputs. (match_main)");
	    }

	    loc = Math.max(0, Math.min(loc, text.length()));
	    if (text.equals(pattern)) {
	      // Shortcut (potentially not guaranteed by the algorithm)
	      return 0;
	    } else if (text.length() == 0) {
	      // Nothing to match.
	      return -1;
	    } else if (loc + pattern.length() <= text.length()
	        && text.substring(loc, loc + pattern.length()).equals(pattern)) {
	      // Perfect match at the perfect spot!  (Includes case of null pattern)
	      return loc;
	    } else {
	      // Do a fuzzy compare.
	      return match_bitap(text, pattern, loc);
	    }
	  }

	  /**
	   * Locate the best instance of 'pattern' in 'text' near 'loc' using the
	   * Bitap algorithm.  Returns -1 if no match found.
	   * @param text The text to search.
	   * @param pattern The pattern to search for.
	   * @param loc The location to search around.
	   * @return Best match index or -1.
	   */
	  protected int match_bitap(String text, String pattern, int loc) {
	    assert (Match_MaxBits == 0 || pattern.length() <= Match_MaxBits)
	        : "Pattern too long for this application.";

	    // Initialise the alphabet.
	    Map<Character, Integer> s = match_alphabet(pattern);

	    // Highest score beyond which we give up.
	    double score_threshold = Match_Threshold;
	    // Is there a nearby exact match? (speedup)
	    int best_loc = text.indexOf(pattern, loc);
	    if (best_loc != -1) {
	      score_threshold = Math.min(match_bitapScore(0, best_loc, loc, pattern),
	          score_threshold);
	      // What about in the other direction? (speedup)
	      best_loc = text.lastIndexOf(pattern, loc + pattern.length());
	      if (best_loc != -1) {
	        score_threshold = Math.min(match_bitapScore(0, best_loc, loc, pattern),
	            score_threshold);
	      }
	    }

	    // Initialise the bit arrays.
	    int matchmask = 1 << (pattern.length() - 1);
	    best_loc = -1;

	    int bin_min, bin_mid;
	    int bin_max = pattern.length() + text.length();
	    // Empty initialization added to appease Java compiler.
	    int[] last_rd = new int[0];
	    for (int d = 0; d < pattern.length(); d++) {
	      // Scan for the best match; each iteration allows for one more error.
	      // Run a binary search to determine how far from 'loc' we can stray at
	      // this error level.
	      bin_min = 0;
	      bin_mid = bin_max;
	      while (bin_min < bin_mid) {
	        if (match_bitapScore(d, loc + bin_mid, loc, pattern)
	            <= score_threshold) {
	          bin_min = bin_mid;
	        } else {
	          bin_max = bin_mid;
	        }
	        bin_mid = (bin_max - bin_min) / 2 + bin_min;
	      }
	      // Use the result from this iteration as the maximum for the next.
	      bin_max = bin_mid;
	      int start = Math.max(1, loc - bin_mid + 1);
	      int finish = Math.min(loc + bin_mid, text.length()) + pattern.length();

	      int[] rd = new int[finish + 2];
	      rd[finish + 1] = (1 << d) - 1;
	      for (int j = finish; j >= start; j--) {
	        int charMatch;
	        if (text.length() <= j - 1 || !s.containsKey(text.charAt(j - 1))) {
	          // Out of range.
	          charMatch = 0;
	        } else {
	          charMatch = s.get(text.charAt(j - 1));
	        }
	        if (d == 0) {
	          // First pass: exact match.
	          rd[j] = ((rd[j + 1] << 1) | 1) & charMatch;
	        } else {
	          // Subsequent passes: fuzzy match.
	          rd[j] = (((rd[j + 1] << 1) | 1) & charMatch)
	              | (((last_rd[j + 1] | last_rd[j]) << 1) | 1) | last_rd[j + 1];
	        }
	        if ((rd[j] & matchmask) != 0) {
	          double score = match_bitapScore(d, j - 1, loc, pattern);
	          // This match will almost certainly be better than any existing
	          // match.  But check anyway.
	          if (score <= score_threshold) {
	            // Told you so.
	            score_threshold = score;
	            best_loc = j - 1;
	            if (best_loc > loc) {
	              // When passing loc, don't exceed our current distance from loc.
	              start = Math.max(1, 2 * loc - best_loc);
	            } else {
	              // Already passed loc, downhill from here on in.
	              break;
	            }
	          }
	        }
	      }
	      if (match_bitapScore(d + 1, loc, loc, pattern) > score_threshold) {
	        // No hope for a (better) match at greater error levels.
	        break;
	      }
	      last_rd = rd;
	    }
	    return best_loc;
	  }

	  /**
	   * Compute and return the score for a match with e errors and x location.
	   * @param e Number of errors in match.
	   * @param x Location of match.
	   * @param loc Expected location of match.
	   * @param pattern Pattern being sought.
	   * @return Overall score for match (0.0 = good, 1.0 = bad).
	   */
	  private double match_bitapScore(int e, int x, int loc, String pattern) {
	    float accuracy = (float) e / pattern.length();
	    int proximity = Math.abs(loc - x);
	    if (Match_Distance == 0) {
	      // Dodge divide by zero error.
	      return proximity == 0 ? accuracy : 1.0;
	    }
	    return accuracy + (proximity / (float) Match_Distance);
	  }

	  /**
	   * Initialise the alphabet for the Bitap algorithm.
	   * @param pattern The text to encode.
	   * @return Hash of character locations.
	   */
	  protected Map<Character, Integer> match_alphabet(String pattern) {
	    Map<Character, Integer> s = new HashMap<Character, Integer>();
	    char[] char_pattern = pattern.toCharArray();
	    for (char c : char_pattern) {
	      s.put(c, 0);
	    }
	    int i = 0;
	    for (char c : char_pattern) {
	      s.put(c, s.get(c) | (1 << (pattern.length() - i - 1)));
	      i++;
	    }
	    return s;
	  }


	  //  PATCH FUNCTIONS


	  /**
	   * Increase the context until it is unique,
	   * but don't let the pattern expand beyond Match_MaxBits.
	   * @param patch The patch to grow.
	   * @param text Source text.
	   */
	  protected void patch_addContext(Patch patch, String text) {
	    if (text.length() == 0) {
	      return;
	    }
	    String pattern = text.substring(patch.start2, patch.start2 + patch.length1);
	    int padding = 0;

	    // Look for the first and last matches of pattern in text.  If two different
	    // matches are found, increase the pattern length.
	    while (text.indexOf(pattern) != text.lastIndexOf(pattern)
	        && pattern.length() < Match_MaxBits - Patch_Margin - Patch_Margin) {
	      padding += Patch_Margin;
	      pattern = text.substring(Math.max(0, patch.start2 - padding),
	          Math.min(text.length(), patch.start2 + patch.length1 + padding));
	    }
	    // Add one chunk for good luck.
	    padding += Patch_Margin;

	    // Add the prefix.
	    String prefix = text.substring(Math.max(0, patch.start2 - padding),
	        patch.start2);
	    if (prefix.length() != 0) {
	      patch.diffs.addFirst(new Diff(Operation.EQUAL, prefix));
	    }
	    // Add the suffix.
	    String suffix = text.substring(patch.start2 + patch.length1,
	        Math.min(text.length(), patch.start2 + patch.length1 + padding));
	    if (suffix.length() != 0) {
	      patch.diffs.addLast(new Diff(Operation.EQUAL, suffix));
	    }

	    // Roll back the start points.
	    patch.start1 -= prefix.length();
	    patch.start2 -= prefix.length();
	    // Extend the lengths.
	    patch.length1 += prefix.length() + suffix.length();
	    patch.length2 += prefix.length() + suffix.length();
	  }

	  /**
	   * Compute a list of patches to turn text1 into text2.
	   * A set of diffs will be computed.
	   * @param text1 Old text.
	   * @param text2 New text.
	   * @return LinkedList of Patch objects.
	   */
	  public LinkedList<Patch> patch_make(String text1, String text2) {
	    if (text1 == null || text2 == null) {
	      throw new IllegalArgumentException("Null inputs. (patch_make)");
	    }
	    // No diffs provided, compute our own.
	    LinkedList<Diff> diffs = diff_main(text1, text2, true);
	    if (diffs.size() > 2) {
	      diff_cleanupSemantic(diffs);
	      diff_cleanupEfficiency(diffs);
	    }
	    return patch_make(text1, diffs);
	  }

	  /**
	   * Compute a list of patches to turn text1 into text2.
	   * text1 will be derived from the provided diffs.
	   * @param diffs Array of Diff objects for text1 to text2.
	   * @return LinkedList of Patch objects.
	   */
	  public LinkedList<Patch> patch_make(LinkedList<Diff> diffs) {
	    if (diffs == null) {
	      throw new IllegalArgumentException("Null inputs. (patch_make)");
	    }
	    // No origin string provided, compute our own.
	    String text1 = diff_text1(diffs);
	    return patch_make(text1, diffs);
	  }

	  /**
	   * Compute a list of patches to turn text1 into text2.
	   * text2 is ignored, diffs are the delta between text1 and text2.
	   * @param text1 Old text
	   * @param text2 Ignored.
	   * @param diffs Array of Diff objects for text1 to text2.
	   * @return LinkedList of Patch objects.
	   * @deprecated Prefer patch_make(String text1, LinkedList<Diff> diffs).
	   */
	  public LinkedList<Patch> patch_make(String text1, String text2,
	      LinkedList<Diff> diffs) {
	    return patch_make(text1, diffs);
	  }

	  /**
	   * Compute a list of patches to turn text1 into text2.
	   * text2 is not provided, diffs are the delta between text1 and text2.
	   * @param text1 Old text.
	   * @param diffs Array of Diff objects for text1 to text2.
	   * @return LinkedList of Patch objects.
	   */
	  public LinkedList<Patch> patch_make(String text1, LinkedList<Diff> diffs) {
	    if (text1 == null || diffs == null) {
	      throw new IllegalArgumentException("Null inputs. (patch_make)");
	    }

	    LinkedList<Patch> patches = new LinkedList<Patch>();
	    if (diffs.isEmpty()) {
	      return patches;  // Get rid of the null case.
	    }
	    Patch patch = new Patch();
	    int char_count1 = 0;  // Number of characters into the text1 string.
	    int char_count2 = 0;  // Number of characters into the text2 string.
	    // Start with text1 (prepatch_text) and apply the diffs until we arrive at
	    // text2 (postpatch_text). We recreate the patches one by one to determine
	    // context info.
	    String prepatch_text = text1;
	    String postpatch_text = text1;
	    for (Diff aDiff : diffs) {
	      if (patch.diffs.isEmpty() && aDiff.operation != Operation.EQUAL) {
	        // A new patch starts here.
	        patch.start1 = char_count1;
	        patch.start2 = char_count2;
	      }

	      switch (aDiff.operation) {
	      case INSERT:
	        patch.diffs.add(aDiff);
	        patch.length2 += aDiff.text.length();
	        postpatch_text = postpatch_text.substring(0, char_count2)
	            + aDiff.text + postpatch_text.substring(char_count2);
	        break;
	      case DELETE:
	        patch.length1 += aDiff.text.length();
	        patch.diffs.add(aDiff);
	        postpatch_text = postpatch_text.substring(0, char_count2)
	            + postpatch_text.substring(char_count2 + aDiff.text.length());
	        break;
	      case EQUAL:
	        if (aDiff.text.length() <= 2 * Patch_Margin
	            && !patch.diffs.isEmpty() && aDiff != diffs.getLast()) {
	          // Small equality inside a patch.
	          patch.diffs.add(aDiff);
	          patch.length1 += aDiff.text.length();
	          patch.length2 += aDiff.text.length();
	        }

	        if (aDiff.text.length() >= 2 * Patch_Margin) {
	          // Time for a new patch.
	          if (!patch.diffs.isEmpty()) {
	            patch_addContext(patch, prepatch_text);
	            patches.add(patch);
	            patch = new Patch();
	            // Unlike Unidiff, our patch lists have a rolling context.
	            // http://code.google.com/p/google-diff-match-patch/wiki/Unidiff
	            // Update prepatch text & pos to reflect the application of the
	            // just completed patch.
	            prepatch_text = postpatch_text;
	            char_count1 = char_count2;
	          }
	        }
	        break;
	      }

	      // Update the current character count.
	      if (aDiff.operation != Operation.INSERT) {
	        char_count1 += aDiff.text.length();
	      }
	      if (aDiff.operation != Operation.DELETE) {
	        char_count2 += aDiff.text.length();
	      }
	    }
	    // Pick up the leftover patch if not empty.
	    if (!patch.diffs.isEmpty()) {
	      patch_addContext(patch, prepatch_text);
	      patches.add(patch);
	    }

	    return patches;
	  }

	  /**
	   * Given an array of patches, return another array that is identical.
	   * @param patches Array of Patch objects.
	   * @return Array of Patch objects.
	   */
	  public LinkedList<Patch> patch_deepCopy(LinkedList<Patch> patches) {
	    LinkedList<Patch> patchesCopy = new LinkedList<Patch>();
	    for (Patch aPatch : patches) {
	      Patch patchCopy = new Patch();
	      for (Diff aDiff : aPatch.diffs) {
	        Diff diffCopy = new Diff(aDiff.operation, aDiff.text);
	        patchCopy.diffs.add(diffCopy);
	      }
	      patchCopy.start1 = aPatch.start1;
	      patchCopy.start2 = aPatch.start2;
	      patchCopy.length1 = aPatch.length1;
	      patchCopy.length2 = aPatch.length2;
	      patchesCopy.add(patchCopy);
	    }
	    return patchesCopy;
	  }

	  /**
	   * Merge a set of patches onto the text.  Return a patched text, as well
	   * as an array of true/false values indicating which patches were applied.
	   * @param patches Array of Patch objects
	   * @param text Old text.
	   * @return Two element Object array, containing the new text and an array of
	   *      boolean values.
	   */
	  public Object[] patch_apply(LinkedList<Patch> patches, String text) {
	    if (patches.isEmpty()) {
	      return new Object[]{text, new boolean[0]};
	    }

	    // Deep copy the patches so that no changes are made to originals.
	    patches = patch_deepCopy(patches);

	    String nullPadding = patch_addPadding(patches);
	    text = nullPadding + text + nullPadding;
	    patch_splitMax(patches);

	    int x = 0;
	    // delta keeps track of the offset between the expected and actual location
	    // of the previous patch.  If there are patches expected at positions 10 and
	    // 20, but the first patch was found at 12, delta is 2 and the second patch
	    // has an effective expected position of 22.
	    int delta = 0;
	    boolean[] results = new boolean[patches.size()];
	    for (Patch aPatch : patches) {
	      int expected_loc = aPatch.start2 + delta;
	      String text1 = diff_text1(aPatch.diffs);
	      int start_loc;
	      int end_loc = -1;
	      if (text1.length() > this.Match_MaxBits) {
	        // patch_splitMax will only provide an oversized pattern in the case of
	        // a monster delete.
	        start_loc = match_main(text,
	            text1.substring(0, this.Match_MaxBits), expected_loc);
	        if (start_loc != -1) {
	          end_loc = match_main(text,
	              text1.substring(text1.length() - this.Match_MaxBits),
	              expected_loc + text1.length() - this.Match_MaxBits);
	          if (end_loc == -1 || start_loc >= end_loc) {
	            // Can't find valid trailing context.  Drop this patch.
	            start_loc = -1;
	          }
	        }
	      } else {
	        start_loc = match_main(text, text1, expected_loc);
	      }
	      if (start_loc == -1) {
	        // No match found.  :(
	        results[x] = false;
	        // Subtract the delta for this failed patch from subsequent patches.
	        delta -= aPatch.length2 - aPatch.length1;
	      } else {
	        // Found a match.  :)
	        results[x] = true;
	        delta = start_loc - expected_loc;
	        String text2;
	        if (end_loc == -1) {
	          text2 = text.substring(start_loc,
	              Math.min(start_loc + text1.length(), text.length()));
	        } else {
	          text2 = text.substring(start_loc,
	              Math.min(end_loc + this.Match_MaxBits, text.length()));
	        }
	        if (text1.equals(text2)) {
	          // Perfect match, just shove the replacement text in.
	          text = text.substring(0, start_loc) + diff_text2(aPatch.diffs)
	              + text.substring(start_loc + text1.length());
	        } else {
	          // Imperfect match.  Run a diff to get a framework of equivalent
	          // indices.
	          LinkedList<Diff> diffs = diff_main(text1, text2, false);
	          if (text1.length() > this.Match_MaxBits
	              && diff_levenshtein(diffs) / (float) text1.length()
	              > this.Patch_DeleteThreshold) {
	            // The end points match, but the content is unacceptably bad.
	            results[x] = false;
	          } else {
	            diff_cleanupSemanticLossless(diffs);
	            int index1 = 0;
	            for (Diff aDiff : aPatch.diffs) {
	              if (aDiff.operation != Operation.EQUAL) {
	                int index2 = diff_xIndex(diffs, index1);
	                if (aDiff.operation == Operation.INSERT) {
	                  // Insertion
	                  text = text.substring(0, start_loc + index2) + aDiff.text
	                      + text.substring(start_loc + index2);
	                } else if (aDiff.operation == Operation.DELETE) {
	                  // Deletion
	                  text = text.substring(0, start_loc + index2)
	                      + text.substring(start_loc + diff_xIndex(diffs,
	                      index1 + aDiff.text.length()));
	                }
	              }
	              if (aDiff.operation != Operation.DELETE) {
	                index1 += aDiff.text.length();
	              }
	            }
	          }
	        }
	      }
	      x++;
	    }
	    // Strip the padding off.
	    text = text.substring(nullPadding.length(), text.length()
	        - nullPadding.length());
	    return new Object[]{text, results};
	  }

	  /**
	   * Add some padding on text start and end so that edges can match something.
	   * Intended to be called only from within patch_apply.
	   * @param patches Array of Patch objects.
	   * @return The padding string added to each side.
	   */
	  public String patch_addPadding(LinkedList<Patch> patches) {
	    short paddingLength = this.Patch_Margin;
	    String nullPadding = "";
	    for (short x = 1; x <= paddingLength; x++) {
	      nullPadding += String.valueOf((char) x);
	    }

	    // Bump all the patches forward.
	    for (Patch aPatch : patches) {
	      aPatch.start1 += paddingLength;
	      aPatch.start2 += paddingLength;
	    }

	    // Add some padding on start of first diff.
	    Patch patch = patches.getFirst();
	    LinkedList<Diff> diffs = patch.diffs;
	    if (diffs.isEmpty() || diffs.getFirst().operation != Operation.EQUAL) {
	      // Add nullPadding equality.
	      diffs.addFirst(new Diff(Operation.EQUAL, nullPadding));
	      patch.start1 -= paddingLength;  // Should be 0.
	      patch.start2 -= paddingLength;  // Should be 0.
	      patch.length1 += paddingLength;
	      patch.length2 += paddingLength;
	    } else if (paddingLength > diffs.getFirst().text.length()) {
	      // Grow first equality.
	      Diff firstDiff = diffs.getFirst();
	      int extraLength = paddingLength - firstDiff.text.length();
	      firstDiff.text = nullPadding.substring(firstDiff.text.length())
	          + firstDiff.text;
	      patch.start1 -= extraLength;
	      patch.start2 -= extraLength;
	      patch.length1 += extraLength;
	      patch.length2 += extraLength;
	    }

	    // Add some padding on end of last diff.
	    patch = patches.getLast();
	    diffs = patch.diffs;
	    if (diffs.isEmpty() || diffs.getLast().operation != Operation.EQUAL) {
	      // Add nullPadding equality.
	      diffs.addLast(new Diff(Operation.EQUAL, nullPadding));
	      patch.length1 += paddingLength;
	      patch.length2 += paddingLength;
	    } else if (paddingLength > diffs.getLast().text.length()) {
	      // Grow last equality.
	      Diff lastDiff = diffs.getLast();
	      int extraLength = paddingLength - lastDiff.text.length();
	      lastDiff.text += nullPadding.substring(0, extraLength);
	      patch.length1 += extraLength;
	      patch.length2 += extraLength;
	    }

	    return nullPadding;
	  }

	  /**
	   * Look through the patches and break up any which are longer than the
	   * maximum limit of the match algorithm.
	   * Intended to be called only from within patch_apply.
	   * @param patches LinkedList of Patch objects.
	   */
	  public void patch_splitMax(LinkedList<Patch> patches) {
	    short patch_size = Match_MaxBits;
	    String precontext, postcontext;
	    Patch patch;
	    int start1, start2;
	    boolean empty;
	    Operation diff_type;
	    String diff_text;
	    ListIterator<Patch> pointer = patches.listIterator();
	    Patch bigpatch = pointer.hasNext() ? pointer.next() : null;
	    while (bigpatch != null) {
	      if (bigpatch.length1 <= Match_MaxBits) {
	        bigpatch = pointer.hasNext() ? pointer.next() : null;
	        continue;
	      }
	      // Remove the big old patch.
	      pointer.remove();
	      start1 = bigpatch.start1;
	      start2 = bigpatch.start2;
	      precontext = "";
	      while (!bigpatch.diffs.isEmpty()) {
	        // Create one of several smaller patches.
	        patch = new Patch();
	        empty = true;
	        patch.start1 = start1 - precontext.length();
	        patch.start2 = start2 - precontext.length();
	        if (precontext.length() != 0) {
	          patch.length1 = patch.length2 = precontext.length();
	          patch.diffs.add(new Diff(Operation.EQUAL, precontext));
	        }
	        while (!bigpatch.diffs.isEmpty()
	            && patch.length1 < patch_size - Patch_Margin) {
	          diff_type = bigpatch.diffs.getFirst().operation;
	          diff_text = bigpatch.diffs.getFirst().text;
	          if (diff_type == Operation.INSERT) {
	            // Insertions are harmless.
	            patch.length2 += diff_text.length();
	            start2 += diff_text.length();
	            patch.diffs.addLast(bigpatch.diffs.removeFirst());
	            empty = false;
	          } else if (diff_type == Operation.DELETE && patch.diffs.size() == 1
	              && patch.diffs.getFirst().operation == Operation.EQUAL
	              && diff_text.length() > 2 * patch_size) {
	            // This is a large deletion.  Let it pass in one chunk.
	            patch.length1 += diff_text.length();
	            start1 += diff_text.length();
	            empty = false;
	            patch.diffs.add(new Diff(diff_type, diff_text));
	            bigpatch.diffs.removeFirst();
	          } else {
	            // Deletion or equality.  Only take as much as we can stomach.
	            diff_text = diff_text.substring(0, Math.min(diff_text.length(),
	                patch_size - patch.length1 - Patch_Margin));
	            patch.length1 += diff_text.length();
	            start1 += diff_text.length();
	            if (diff_type == Operation.EQUAL) {
	              patch.length2 += diff_text.length();
	              start2 += diff_text.length();
	            } else {
	              empty = false;
	            }
	            patch.diffs.add(new Diff(diff_type, diff_text));
	            if (diff_text.equals(bigpatch.diffs.getFirst().text)) {
	              bigpatch.diffs.removeFirst();
	            } else {
	              bigpatch.diffs.getFirst().text = bigpatch.diffs.getFirst().text
	                  .substring(diff_text.length());
	            }
	          }
	        }
	        // Compute the head context for the next patch.
	        precontext = diff_text2(patch.diffs);
	        precontext = precontext.substring(Math.max(0, precontext.length()
	            - Patch_Margin));
	        // Append the end context for this patch.
	        if (diff_text1(bigpatch.diffs).length() > Patch_Margin) {
	          postcontext = diff_text1(bigpatch.diffs).substring(0, Patch_Margin);
	        } else {
	          postcontext = diff_text1(bigpatch.diffs);
	        }
	        if (postcontext.length() != 0) {
	          patch.length1 += postcontext.length();
	          patch.length2 += postcontext.length();
	          if (!patch.diffs.isEmpty()
	              && patch.diffs.getLast().operation == Operation.EQUAL) {
	            patch.diffs.getLast().text += postcontext;
	          } else {
	            patch.diffs.add(new Diff(Operation.EQUAL, postcontext));
	          }
	        }
	        if (!empty) {
	          pointer.add(patch);
	        }
	      }
	      bigpatch = pointer.hasNext() ? pointer.next() : null;
	    }
	  }

	  /**
	   * Take a list of patches and return a textual representation.
	   * @param patches List of Patch objects.
	   * @return Text representation of patches.
	   */
	  public String patch_toText(List<Patch> patches) {
	    StringBuilder text = new StringBuilder();
	    for (Patch aPatch : patches) {
	      text.append(aPatch);
	    }
	    return text.toString();
	  }

	  /**
	   * Parse a textual representation of patches and return a List of Patch
	   * objects.
	   * @param textline Text representation of patches.
	   * @return List of Patch objects.
	   * @throws IllegalArgumentException If invalid input.
	   */
	  public List<Patch> patch_fromText(String textline)
	      throws IllegalArgumentException {
	    List<Patch> patches = new LinkedList<Patch>();
	    if (textline.length() == 0) {
	      return patches;
	    }
	    List<String> textList = Arrays.asList(textline.split("\n"));
	    LinkedList<String> text = new LinkedList<String>(textList);
	    Patch patch;
	    Pattern patchHeader
	        = Pattern.compile("^@@ -(\\d+),?(\\d*) \\+(\\d+),?(\\d*) @@$");
	    Matcher m;
	    char sign;
	    String line;
	    while (!text.isEmpty()) {
	      m = patchHeader.matcher(text.getFirst());
	      if (!m.matches()) {
	        throw new IllegalArgumentException(
	            "Invalid patch string: " + text.getFirst());
	      }
	      patch = new Patch();
	      patches.add(patch);
	      patch.start1 = Integer.parseInt(m.group(1));
	      if (m.group(2).length() == 0) {
	        patch.start1--;
	        patch.length1 = 1;
	      } else if (m.group(2).equals("0")) {
	        patch.length1 = 0;
	      } else {
	        patch.start1--;
	        patch.length1 = Integer.parseInt(m.group(2));
	      }

	      patch.start2 = Integer.parseInt(m.group(3));
	      if (m.group(4).length() == 0) {
	        patch.start2--;
	        patch.length2 = 1;
	      } else if (m.group(4).equals("0")) {
	        patch.length2 = 0;
	      } else {
	        patch.start2--;
	        patch.length2 = Integer.parseInt(m.group(4));
	      }
	      text.removeFirst();

	      while (!text.isEmpty()) {
	        try {
	          sign = text.getFirst().charAt(0);
	        } catch (IndexOutOfBoundsException e) {
	          // Blank line?  Whatever.
	          text.removeFirst();
	          continue;
	        }
	        line = text.getFirst().substring(1);
	        line = line.replace("+", "%2B");  // decode would change all "+" to " "
	        try {
	          line = URLDecoder.decode(line, "UTF-8");
	        } catch (UnsupportedEncodingException e) {
	          // Not likely on modern system.
	          throw new Error("This system does not support UTF-8.", e);
	        } catch (IllegalArgumentException e) {
	          // Malformed URI sequence.
	          throw new IllegalArgumentException(
	              "Illegal escape in patch_fromText: " + line, e);
	        }
	        if (sign == '-') {
	          // Deletion.
	          patch.diffs.add(new Diff(Operation.DELETE, line));
	        } else if (sign == '+') {
	          // Insertion.
	          patch.diffs.add(new Diff(Operation.INSERT, line));
	        } else if (sign == ' ') {
	          // Minor equality.
	          patch.diffs.add(new Diff(Operation.EQUAL, line));
	        } else if (sign == '@') {
	          // Start of next patch.
	          break;
	        } else {
	          // WTF?
	          throw new IllegalArgumentException(
	              "Invalid patch mode '" + sign + "' in: " + line);
	        }
	        text.removeFirst();
	      }
	    }
	    return patches;
	  }


	  /**
	   * Class representing one diff operation.
	   */
	  public static class Diff {
	    /**
	     * One of: INSERT, DELETE or EQUAL.
	     */
	    public Operation operation;
	    /**
	     * The text associated with this diff operation.
	     */
	    public String text;

	    /**
	     * Constructor.  Initializes the diff with the provided values.
	     * @param operation One of INSERT, DELETE or EQUAL.
	     * @param text The text being applied.
	     */
	    public Diff(Operation operation, String text) {
	      // Construct a diff with the specified operation and text.
	      this.operation = operation;
	      this.text = text;
	    }

	    /**
	     * Display a human-readable version of this Diff.
	     * @return text version.
	     */
	    public String toString() {
	      String prettyText = this.text.replace('\n', '\u00b6');
	      return "Diff(" + this.operation + ",\"" + prettyText + "\")";
	    }

	    /**
	     * Create a numeric hash value for a Diff.
	     * This function is not used by DMP.
	     * @return Hash value.
	     */
	    @Override
	    public int hashCode() {
	      final int prime = 31;
	      int result = (operation == null) ? 0 : operation.hashCode();
	      result += prime * ((text == null) ? 0 : text.hashCode());
	      return result;
	    }

	    /**
	     * Is this Diff equivalent to another Diff?
	     * @param obj Another Diff to compare against.
	     * @return true or false.
	     */
	    @Override
	    public boolean equals(Object obj) {
	      if (this == obj) {
	        return true;
	      }
	      if (obj == null) {
	        return false;
	      }
	      if (getClass() != obj.getClass()) {
	        return false;
	      }
	      Diff other = (Diff) obj;
	      if (operation != other.operation) {
	        return false;
	      }
	      if (text == null) {
	        if (other.text != null) {
	          return false;
	        }
	      } else if (!text.equals(other.text)) {
	        return false;
	      }
	      return true;
	    }

		public Operation getOperation() {
			return operation;
		}

		public void setOperation(Operation operation) {
			this.operation = operation;
		}

		public String getText() {
			return text;
		}

		public void setText(String text) {
			this.text = text;
		}
	    
	    public String getOperationStr(){
	    	return operation.name();
	    }
	  }


	  /**
	   * Class representing one patch operation.
	   */
	  public static class Patch {
	    public LinkedList<Diff> diffs;
	    public int start1;
	    public int start2;
	    public int length1;
	    public int length2;

	    /**
	     * Constructor.  Initializes with an empty list of diffs.
	     */
	    public Patch() {
	      this.diffs = new LinkedList<Diff>();
	    }

	    /**
	     * Emmulate GNU diff's format.
	     * Header: @@ -382,8 +481,9 @@
	     * Indicies are printed as 1-based, not 0-based.
	     * @return The GNU diff string.
	     */
	    public String toString() {
	      String coords1, coords2;
	      if (this.length1 == 0) {
	        coords1 = this.start1 + ",0";
	      } else if (this.length1 == 1) {
	        coords1 = Integer.toString(this.start1 + 1);
	      } else {
	        coords1 = (this.start1 + 1) + "," + this.length1;
	      }
	      if (this.length2 == 0) {
	        coords2 = this.start2 + ",0";
	      } else if (this.length2 == 1) {
	        coords2 = Integer.toString(this.start2 + 1);
	      } else {
	        coords2 = (this.start2 + 1) + "," + this.length2;
	      }
	      StringBuilder text = new StringBuilder();
	      text.append("@@ -").append(coords1).append(" +").append(coords2)
	          .append(" @@\n");
	      // Escape the body of the patch with %xx notation.
	      for (Diff aDiff : this.diffs) {
	        switch (aDiff.operation) {
	        case INSERT:
	          text.append('+');
	          break;
	        case DELETE:
	          text.append('-');
	          break;
	        case EQUAL:
	          text.append(' ');
	          break;
	        }
	        try {
	          text.append(URLEncoder.encode(aDiff.text, "UTF-8").replace('+', ' '))
	              .append("\n");
	        } catch (UnsupportedEncodingException e) {
	          // Not likely on modern system.
	          throw new Error("This system does not support UTF-8.", e);
	        }
	      }
	      return unescapeForEncodeUriCompatability(text.toString());
	    }
	  }

	  /**
	   * Unescape selected chars for compatability with JavaScript's encodeURI.
	   * In speed critical applications this could be dropped since the
	   * receiving application will certainly decode these fine.
	   * Note that this function is case-sensitive.  Thus "%3f" would not be
	   * unescaped.  But this is ok because it is only called with the output of
	   * URLEncoder.encode which returns uppercase hex.
	   *
	   * Example: "%3F" -> "?", "%24" -> "$", etc.
	   *
	   * @param str The string to escape.
	   * @return The escaped string.
	   */
	  private static String unescapeForEncodeUriCompatability(String str) {
	    return str.replace("%21", "!").replace("%7E", "~")
	        .replace("%27", "'").replace("%28", "(").replace("%29", ")")
	        .replace("%3B", ";").replace("%2F", "/").replace("%3F", "?")
	        .replace("%3A", ":").replace("%40", "@").replace("%26", "&")
	        .replace("%3D", "=").replace("%2B", "+").replace("%24", "$")
	        .replace("%2C", ",").replace("%23", "#");
	  }
}
